Effects of Saccharomyces cerevisiae boulardii on preweaning calf performance in the presence and absence of chronic stress

The objectives of this study were to evaluate the effects of a Saccharomyces cerevisiae boulardii CNCM I-1079 probiotic yeast product (PRO) on the performance, health, and stress resilience of Holstein heifer calves in the presence and absence of chronic stress (CS). Chronic stress was simulated by inconsistency in the delivery of the calf milk replacer. A total of 80 Holstein heifer calves were randomly assigned to 1 of 4 treatments at 5 d of age: calves that were not exposed to any CS and did not receive PRO (noCS-noPRO, n = 20), calves exposed to CS and not receiving PRO (CS-noPRO, n = 20), calves not exposed to any CS and that did receive PRO (noCS-PRO, n = 20), or calves that were exposed to CS and received PRO (CS-PRO, n = 20). Starter intake was recorded daily, and BW were measured weekly to determine calf performance. Fecal scores were recorded weekly, and blood samples were obtained every 2 wk to monitor calf health. Additionally, fecal glucocorticoid metabolites (fGCM) were measured to identify stress responses in calves. Calves that were exposed to CS consumed less starter feed and had lower mean BW compared with calves that were not. Calves receiving PRO showed an improvement in calf starter intake and were able to mitigate the effects of CS on BW. It was found that PRO influenced the lymphocyte count by increasing it over time, and CS influenced the neutrophil count by increasing it. Calves that were continuously exposed to inconsistent diet distribution had higher mean fGCM during the preweaning phase, whereas calves receiving PRO had lower mean fGCM concentrations. In conclusion, inconsistent diet distribution likely exposed calves to CS, as it was shown to repeatedly induce stress responses in calves. Calves receiving PRO were able to mitigate the negative effects of CS; however, no benefits of PRO were observed in well-managed calves not exposed to chronic stress. Therefore, we predict that PRO administration may help promote appropriate coping behaviors and stress resilience in calves and can be used as a supportive strategy during challenging times.